1. Field
This application relates generally to methods for detecting and, in particular, to methods for detecting the concentration and capacity of antioxidants in a sample.
2. Background of the Technology
Antioxidants such as vitamin C from fruits and vegetables provide a crucial protection capacity to fight free radicals which are implicated in the development of more than fifty diseases. Determination of antioxidant concentration in foods or other biological systems, including blood, is of great importance [1-7].
There are various methods for measuring vitamin C including conventional iodometric titration [2], spectrophotometric methods [3], chromatographic methods [4,5], and electrochemical methods [6,7]. These methods often involve several steps or multi chemical agents for concentration determination. They are time-consuming and the detection limit is usually at about μM levels or higher [4-7].
There is also great interest in determining total antioxidant capacity [8,9]. Representative methods include the oxygen radical absorbance capacity (ORAC) assay for antioxidant potency measurement [8,9]. The ORAC assay uses a fluorescent probe whose fluorescence decay is an indication of damage from its reaction with a free radical such as peroxyl radicals [8,9]. The inhibition of free radical damage by an antioxidant, as reflected in the protection against the fluorescence decay in the ORAC assay, is a measure of the antioxidant capacity of the antioxidant against the free radical [8,9]. However, there are certain drawbacks to using this method. First, the sample size required is usually relatively large, more than 1 gram for solids and >50 mL for liquids. In addition, the fluorescent probes emit visible light, a region where other biospecies may emit, thus causing interference. The probes may be subjected to photobleach, and they are damaged by free radicals and are therefore not reusable. The probes may not work with both hydrophilic and hydrophobic antioxidants so specific probes have to be designed for a particular application. In addition, the sensitivity is low and not suitable for in vivo applications.
Accordingly, there still exists a need for improved methods for antioxidant detection.